The present invention relates to light pens and pertains particularly to a parallax free light pen having means for eliminating parallax between the receptor of the light pen and an interactive light source.
Cathode ray type display devices and interrelated light guns or light pens have been in extensive use for some time. Such display screens have been frequently used to display specific items such as a geographical area with the use of a light gun or light pen interconnected with an associated processing device and further display means for selecting and displaying certain items of information relative to specific items pin-pointed on the larger display. The so-called light pen constitutes a receptor for receiving light from the display tube and initiating a signal for recall and display of reference data related to the specific point of reference, selected by the light pen. In order for the receptor to perform its functions satisfactorily of detecting a specific item of display without confusing the item with surrounding items it is necessary that the receptor be accurately aligned with the light source to remove or eliminate parallax.
While there are many suggestions for overcoming the problem with parallax with other optical and electro-optical systems, a satisfactory solution has not been proposed for the problems associated with the systems such as considered herein. It is desirable that any apparatus for solving such problems be simple, inexpensive and reliable in its operation.